1. Field of the Invention
The invention relates to a process of inhibiting the polymerization of vinylaromatic or vinylaliphatic compounds, especially styrene, during distillation.
2. Discussion of the Background
Styrene is the starting product for the preparation of polystyrene and mixed polymers. Due to the incomplete reaction and formation of by-products in the preparation of styrene, distillative separation is necessary. Since the styrene easily polymerizes thermally at the distillation temperatures, an inhibitor must be added to the process. Such inhibitors, e.g., nitrophenols, nitrosophenols, p-tert-butylpyrocatechol, or sulfur, are known and are also used on a large scale. From the publications U.S. Pat. No. 4,967,027 and European Patent No. B-0,229,515, it can be further concluded that combinations of different inhibitors can also be used.
Due to its thermal sensitivity, on a large scale, styrene is distilled in vacuum without exception. It is known that most inhibitors need the presence of oxygen to be effective.
In principle, this produces the problem of making available sufficient oxygen in a column operated in vacuum.
There is therefore a need for new polymerization inhibitors for vinylaromatic or vinylaliphatic compounds that are suitable for use at increased temperatures as they are used under distillation conditions and that do not have the indicated disadvantages.